Intrinsic Mechanism for Carbon Dioxide Methanation over Ru-Based Nanocatalysts

Ruthenium-based supported catalysts are of great potential for CO2 methanation, while the catalytic mechanisms remain elusive owing to the conjunction of the metal size and support effect, as well as the possible strong metal/support interactions (SMSI) in a practical catalyst. Herein, with the deposition of alumina over the Ru/SiC model nanocatalysts by the method of the atomic layer deposition (ALD) technique, the corrugated (1011) surface of Ru nanoparticles can be selectively insulated due to its preference for alumina deposition, and the intrinsic activity of CO2 conversion was confirmed to depend crucially on the residual planar (0001) surface. Characterizations including in situ infrared spectroscopy (IR) combined with density functional theory (DFT) calculation and the microkinetic modeling revealed that the competitive kinetics of H2 and CO2 activation on the Ru surface governs the activity and selectivity of methanation. The terrace sites of Ru nanocatalysts serve as the genuine active site through the HCOO* intermediate with the surface occupied by the H* species for further methanation. The (1011) surface suffers from a lower capability for hydrogenation due to its preference toward CO2 adsorption and results in the surface poisoning by the *C and *CH species, which thus makes it a negligible contribution toward methanation over Ru nanocatalysts. However, the presence of the alumina overlayer on the corrugated surface also improves the stability of the Ru nanocatalyst, to keep its activity even at a high temperature pretreatment. Our results demonstrate the terrace sites as the intrinsic active sites for CO2 methanation and also deepen insights on the catalytic mechanism of CO2 transformation over Ru-based nanocatalysts.